I also am beginning to finish my bathroom in the basement with the same configuration this guy has. My question is since these pipes are all buried in the concrete slab, are they already vented or do I have to run pipes up through two floors to reach the roof? I saw the same house being built and they have the waste drain flowing about 6-8 feet to a y fitting tying it into the main waste pipe located across the basement. However these are all eventually covered with concrete. Is the sink supposed to drain into the shower drain? The builder told me that the 2" dia. pipe was for the sink, one 2" dia. pipe for the shower and a 4" dia pipe for the toilet. Could he have been mistaken and meant the the sink pipe was a vent? Thanks!